1. Field of the Invention
The present invention relates generally to clutch devices suitable for motorcycles or the like. In particular, the invention relates to a clutch device configured to use hydraulic pressure produced in response to the manual operation of a clutch lever by a rider (operator) to engage and disengage a clutch mechanism.
2. Description of Background Art
Motorcycles or the like generally use a configuration in which a left one of handlebars is provided with a manually operated clutch lever, which is gripped with a rider's left hand to operatively engage and disengage a clutch mechanism. In such a clutch device, the clutch mechanism usually undergoes a spring force or the like to come into an engagement state. When starting or shifting, a rider grips the clutch lever with a hand to disengage and engage the clutch mechanism. This needs gripping power to release the clutch mechanism against the spring force to engage the clutch mechanism. It is expected to reduce the operation force for female riders having small gripping power. It can be said that it is effective to reduce such an operation force particularly in large-sized motorcycles which needs large clutch capacity and has a large clutch engaging force.
In view of the forgoing, for instance, each of Japanese Patent Laid-open No. Hei 8-133169, Japanese Patent No. 2874481, Japanese Patent Laid-open No. Hei 6-117450, and Japanese Patent Laid-open No. 2005-248976 disclose a devices configured to assist clutch lever operation for releasing a clutch mechanism.
Among them, an assist device of Japanese Patent Laid-open No. Hei 8-133169, for instance, is configured to apply pressurized oil for forcibly lubricating the inside of an engine to a plunger, which presses a push rod to the release side to release the clutch mechanism, thus providing an assist force for the release side (that is, an assist force on the side of manually operating the clutch lever).
Use of such an assist device can alleviate the problem as mentioned above. However, the assist device disclosed in Japanese Patent Laid-open No. Hei 8-133169 is configured to use the lubricating pressure of the engine to provide an assist force. The assist device is influenced by engine rotation, lubricating oil, etc. to vary in assist force. Thus, there arises a problem in that it is difficult to provide a stable assist force.
The assist device of Japanese Patent No. 2874481 is configured such that a clutch cable connected to a clutch lever is wound around a rotary body driven by a motor and the assist device assists the operation force of the clutch lever when the clutch mechanism is released by operating the clutch lever. As mentioned above, this conventional assist device is configured to assist the operation force of the clutch lever operated. Therefore, if the so-called auto-clutch mechanism is used in which shift change is performed only by operating a shift pedal without operating the clutch lever, then the clutch mechanism cannot be released by the assist force of the assist device as mentioned earlier.
Further, the magnitude of an assist force is set at a constant level in the conventional assist device. If the assist force is set at a level greater than gripping power, the reaction force applied to the rider who is operating the clutch lever is smaller than the assist force set at a level greater than the gripping power. In such a case, some riders may feel a void since they feel the operation of the clutch lever to be light. Therefore, a configuration has been desired in which the setting of the assist force can be changed according to the rider's preference. For example, a configuration has been desired in which the magnitude of the assist force can be set at a small level for the rider having large hands or large gripping power.
In view of the foregoing, it is an object of the present invention is to provide a clutch device that is provided with an assist device configured to change the setting of the magnitude of an assist force according to a rider's preference.